1. Field of the Invention
This invention relates generally to a control method for an engine in a motor vehicle and, more specifically to a method of adjusting the spark timing sequence for reducing loading variations on an internal combustion engine.
2. Discussion of the Related Art
One of the most notable examples of change in the automotive industry has been the improvement in the fuel efficiency of the internal combustion engine. This improvement was made possible, largely by the reduction in the size of the internal combustion engine. Although the reduction in the size of the internal combustion engine has created a benefit by increasing fuel efficiency, it has also created a problem.
The operation of an automotive air conditioning unit best illustrates this problem. The typical automotive air conditioning unit uses a compressor to perform the cooling function. When the air conditioning unit cycles power, the compressor creates a torque that opposes the torque generated by the internal combustion engine of a vehicle. This, in turn, causes a deceleration in the speed of the internal combustion engine. Typically a series of oscillations also follow as the engine controller tries to compensate for the initial deceleration. This loading variation problem was not readily noticed when large engines were predominant in vehicles, since the torque created by the compressor of the air conditioning unit was very small in comparison with the torque generated by a large engine. However the large engine is no longer the norm in todays automobile and the smaller engines, which are used in place of the larger engines, have a much smaller torque output so that the torque created by the air conditioning unit is a larger amount relative to the torque generated by the smaller engine. Thus deceleration and oscillations that are created by the air conditioning unit cycling power are more of a problem today since current vehicles are more likely to have smaller engines.
A number of methods have been attempted to correct the problem. In particular the size of the compressor has been reduced in order to lessen the effect of the torque created by the air conditioning unit. However, reducing the size of the compressor creates a undesirable reduction in the ability of the air conditioning unit to cool the vehicle. Another approach has been attempted such that half of the compressor actuates first and the other half of the compressor actuates some time after the first half of the compressor has started, thus lessening the overall torque effect of the cycling of power of the air conditioning unit on the internal combustion engine. However, due to the special design, the dual starting air conditioning unit costs more than a standard air conditioning unit and thus is not a viable solution for many automotive manufacturers.
Therefore, it would be desirable to provide a methodology for reducing the effect that a cycling of power of the automotive air conditioning unit has on the operation of the vehicle.